Polymer grout compositions are often used to consolidate soils around underground structures like concrete tanks and pools, sewer pipes, gas and water mains, and manholes. Typically, cementitious, urethane, and acrylamide grouts provide strong, tough composities useful for this purpose, but the composite soil is very difficult to re-enter or to break up if one needs to move or dig into the area. Recently, there has been increased interest in using polymer grout compositions as part of the closure system of shallow subsurface structures for disposal of solid wastes. In this application, the grout must be of sufficiently low viscosity that it can be applied by injection or gravity feed, and should provide good water and chemical resistance to the consolidated waste area, but the consolidated structure should also be friable so that it can be readily re-entered and broken up at a later date for inspection or removal of the wastes to an alternate disposal site.
Polyurethane prepolymer compositions have long been used for soil consolidation and as grouts for sealing structures. U.S. Pat. No. 3,985,588 to Speech is directed to a foam polyurethane grout that is typically pumped into a sewer line to seal joints. U.S. Pat. No. 3,719,050 to Asao, et. al, describes a polyurethane prepolymer composition that is a gel rather than a foam. A chemical soil consolidation composition utilizing a water immiscible solvent is "Scotch-Seal 5620"Chemical Grout, commercially available from 3M Company, St. Paul, Minn., which is an 80% polyurethane prepolymer in butyl benzyl phthlate. This composition has a high initial viscosity (about 6,000 centipoise), but has a low viscosity when mixed with water at about a 10:1 to 20:1 water/composition ratio to allow good soil penetration. Because of the high initial viscosity, this composition is not easily pumpable through standard grout pumping equipment and thus cannot be used for many injectable applications. U.S. Pat. Nos. 5,037,879, 5,102,938, and 5,229,453 to Roberts describe alternate polyurethane prepolymer systems that react with water to produce a gel for use in sealing water containing structures and soil stabilization.
Urethane-based grout systems typically do not weather well and break down when exposed to ultra violet radiation, acid solutions, strong organic solvents, and radioactive environments. They also typically shrink as they dry out and often give a porous structure that does not provide adequate protection against water penetration in waste sites. They also have fast gel times, typically only a few minutes, and thus are not suitable for deep penetration applications. The present invention provides an alternate polymer grout composition that is, in a preferred embodiment, of low viscosity so that it is easily injectable, is durable and imparts good water and chemical resistance to the consolidated soil area, and remains hand-breakable after curing so that the consolidated soil can be re-entered at a later date.